Both the Simple.Connect() and Modem.CreateBearer() are updated to
allow a new 'multiplex' setting in the properties provided by the user
in both of these methods.
The new setting expects a MMBearerMultiplexSupport enum indicating
what kind of multiplex needs the user has:
* none: if multiplex must not be used.
* requested: if multiplex should be used if available.
* required: if multiplex must be used.
The underlying implementations will take care of accepting or
rejecting the setting depending on the system and modem capabilities.
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